Right outside the Vancouver Convention and Exhibition Centre - currently hosting the third World Urban Forum - a house is being built in a day.

The group's aim is to build communities over time

In a scene vaguely reminiscent of the film Witness, blue-shirted men and women swarm over the wooden skeleton, as, complete with windowboxes, the bungalow rises up on the pavement.

Minus its roof - which will take too long to assemble - it will stay there until Friday, when it will be dismantled and sent to Louisiana to house a family made homeless by Hurricane Katrina.

The group behind the house is the Greater Vancouver part of Habitat For Humanity, a Canadian non-governmental organisation that is building houses in 100 countries around the world.

The group's executive director, Anneke Rees, told BBC News that putting the house up demonstrates their aim of "giving people who could never afford to buy their own home the opportunity to get into that life".

"You can do a lot of things when a community comes together," she added.

"People can do it if they take action, as opposed to talking about it."

Cost of buying

This house is actually the second one to be involved in the Hurricane Katrina relief effort - the first was built in Ottawa and sent down to the US in February.

It is part of a project called Operation Home Delivery.

"The ability to build is not the issue - the issue is land, no matter what country you're in"

Anneke Rees, Habitat for Humanity

"We're not in the business of disaster relief - our business is to build communities over time," Ms Rees said.

"But after the tsunami and after the hurricanes, we were approached by a lot of organisations, because they know we can do it. They came to Habitat and said, 'what can you do to help us?'"

Habitat For Humanity is one of several groups making a point at the World Urban Forum about the high cost of buying somewhere to live in the modern world.

A number of factors are behind this. With more and more people migrating to cities - and only a finite space in which they can live - house prices are soaring, particularly in the West.

Habitat For Humanity is building houses in 100 countries

Indeed, the Greater Vancouver group's first project - a set of 27 houses in the nearby town of Burnaby - was designed to tackle this problem directly.

Families keen to buy a house but without the funds to do so have been able to try to become a "partner family" with the group.

If successful, they can buy the house at no profit and financed with interest-free mortgages, in exchange for "sweat equity" - putting 500 hours of effort into building the houses in the first place.

"It involves them - it makes them have the feeling that they're not just getting something; they worked very hard to get it," Ms Rees explained.

"They become just like any other homeowner."

Land issue

In all, Habitat For Humanity is building 200,000 houses around the world.

But despite this, Ms Rees said the group was unable to do as much work as it would like because land remains prohibitively expensive.

"The ability to build is not the issue - the issue is land, no matter what country you're in," she said.